ddl: ignore integer zerofill size attribute when changing the column types (#20862)

[ti-srebot]

cherry-pick #20862 to release-4.0

---

What problem does this PR solve?

Issue Number: close #20529

What is changed and how it works?

how does it work?

Like int(3), bigint(2), the number enclosed will be stored as flen in the field type, while it shouldn't be concerned when we make column type change from int(3) to(2) . Because bigint is quite larger than int, there is no need to take a reorg process.

what is changed

We should use the default flen of the specified field type rather than the origin flen.

Check List

Tests

• Unit test
• Integration test

Release note

• ddl: ignore integer zerofill size attribute when changing the column types

[ti-srebot]

/run-all-tests

[bb7133]

@AilinKid Please resolve the conflicts.

[zz-jason]

@AilinKid please fix the build:

[2020-11-11T07:23:49.371Z] # github.com/pingcap/tidb/ddl

[2020-11-11T07:23:49.371Z] ddl/column.go:355:1: syntax error: non-declaration statement outside function body

[2020-11-11T07:23:49.371Z] ddl/column.go:363:1: syntax error: unexpected ==, expecting }

[2020-11-11T07:23:49.371Z] ddl/column.go:441:1: syntax error: unexpected >>, expecting }

[2020-11-11T07:23:49.371Z] ddl/column.go:441:98: invalid character U+0023 '#'

[2020-11-11T07:23:49.371Z] make: *** [importer] Error 2

[2020-11-11T07:23:49.933Z] # github.com/pingcap/tidb/ddl

[2020-11-11T07:23:49.933Z] ddl/column.go:355:1: syntax error: non-declaration statement outside function body

[2020-11-11T07:23:49.933Z] ddl/column.go:363:1: syntax error: unexpected ==, expecting }

[2020-11-11T07:23:49.933Z] ddl/column.go:441:1: syntax error: unexpected >>, expecting }

[2020-11-11T07:23:49.933Z] ddl/column.go:441:98: invalid character U+0023 '#'

[2020-11-11T07:23:49.933Z] make: *** [server] Error 2

[2020-11-11T07:23:49.933Z] # github.com/pingcap/tidb/ddl

[2020-11-11T07:23:49.933Z] ddl/column.go:355:1: syntax error: non-declaration statement outside function body

[2020-11-11T07:23:49.933Z] ddl/column.go:363:1: syntax error: unexpected ==, expecting }

[2020-11-11T07:23:49.933Z] ddl/column.go:441:1: syntax error: unexpected >>, expecting }

[2020-11-11T07:23:49.933Z] ddl/column.go:441:98: invalid character U+0023 '#'

[2020-11-11T07:23:49.933Z] make: *** [server] Error 2

[AilinKid]

/run-all-tests

[AilinKid]

/run-tics-test

[AilinKid]

/run-sqllogic-test-2

[AilinKid]

/run-unit-test

[AilinKid]

/run-tics-test

[AilinKid]

/run-tics-test

[AilinKid]

/run-unit-test

[bb7133]

LGTM

[wjhuang2016]

lgtm